The present invention relates to a dosimeter glass element which generates fluorescence corresponding to the radiation exposure dose thereof upon excitation by ultraviolet light, and more particularly, to a small-sized bar-shaped dosimeter glass element, a method for manufacturing same, and a dosimeter holder suitable for accommodating a small-sized dosimeter glass element.
In the installation and operation of facilities such as nuclear reactors, accelerators, X-ray generators, and radio isotopes, it is necessary to achieve complete safety in radiation management, in order to protect human beings from radioactivity. In particular, management must be provided to ensure that the radiation dose to which the employees working in various fields in the aforementioned facilities, and the users of the facilities, are exposed comes within a prescribed tolerance range. Dosimeters are used for radiation management of this kind. These dosimeters are located in prescribed locations within a facility, and/or are carried by employees and users, and by reading out the respective exposure doses thereof at regular intervals, it is possible to manage the radiation doses to which employees and users are exposed.
One type of generally used dosimeter is a fluorescent glass dosimeter. In general, a fluorescent glass dosimeter uses glass elements made from phosphate glass containing silver ions. After being irradiated with radiation and activated, these glass elements generate a phenomenon (radio photo luminescence: RPL) whereby they produce fluorescence when excited by ultraviolet radiation of wavelength 300-400 nm. Since the intensity of the fluorescence produced is directly proportional to the radiation exposure dose received by the glass element, it is possible to measure the radiation exposure dose by detecting the intensity of the fluorescence. A particular feature of fluorescent glass dosimeters of this kind is that they can be read out repeatedly, without the core which generates RPL being destroyed by the reading operation.
In recent years, small-sized fluorescent glass dosimeters have been used in dose evaluation for radiation therapy and diagnosis, dose measurement in animal experiments, precise dose distribution measurement and other various types of experiments, and the like. In measurement using small-sized fluorescent glass dosimeters of this kind, the dosimeter glass elements used are very small bar-shaped members. Conventionally, these dosimeter glass elements are fabricated by taking a silver-activated phosphate glass base material that has been formed by melting into a block shape, slicing it into square bar shapes slightly larger than the final shape, and then polishing all the faces thereof until it assumes the final shape. When fabricating a cylindrical glass element, after slicing to a square bar shape slightly larger than the final shape, it is then processed to achieve a circular bar shape, whereupon all faces thereof are polished to achieve the final shape.
However, in the conventional method for manufacturing a fluorescent glass element described above, since the material is melted to form a block shape, then sliced into square bar shapes, and then polished on all faces to assume the final shape, the number of processes is large, and the manufacturing time and manufacturing costs are considerable. The process of polishing on all faces, in particular, leads to increased labour and cost.
Moreover, the small-sized fluorescent glass dosimeter described above is normally positioned on a measurement object in a state where the fluorescent glass element is accommodated in a dosimeter holder. This dosimeter holder is generally a tubular vessel having a cap and bearing a holder ID which is the same as the identification ID applied to the fluorescent glass element, marked on the surface thereof. When a fluorescent glass dosimeter is accommodated in a dosimeter holder of this kind, placed on a measurement object, and then irradiated locally by radiation, for example, irradiated by a spot of approximately 1 mm diameter, the range of the fluorescent glass element therein that is exposed to radiation must match the range of fluorescence reading performed by the fluorescence reading device.
However, with a conventional dosimeter holder, it has not been possible to confirm, from an external position, the central position of the fluorescence reading range of the fluorescent glass element accommodated in the dosimeter holder, and hence it has not been possible to tell if the radiation exposure range and the fluorescence reading range can be matched by positioning the holder on the measurement object using a point of the dosimeter holder as a reference. Moreover, since the fluorescence reading range of the fluorescent glass element accommodated inside the dosimeter holder cannot be told, it has not been possible to match the position of radiation exposure, by an experiment lamp, or the like, accurately, with the fluorescence reading range. Consequently, in some cases, divergence occurs between the radiation exposure range and the fluorescence reading range, and hence the irradiated amount of radiation cannot be measured accurately.
The present invention has been devised with a view to resolving the aforementioned problems of the prior art, a first object thereof being to provide a dosimeter glass element and method for manufacturing same, whereby a dosimeter glass element can be manufactured by a small number of steps, in a short period of time, and at low cost.
Moreover, it is a second object of the present invention to provide a dosimeter holder whereby positioning in a measurement object can be performed readily and accurately, in such a manner that the position of radiation exposure can be matched to the position at which the fluorescence of the dosimeter glass element accommodated in the dosimeter holder is read out.
In order to achieve the first object, the present invention provides a method for manufacturing a dosimeter glass element which generates fluorescence corresponding to the radiation exposure dose thereof upon excitation by ultraviolet light, comprising: heating and extending a cylindrical glass base material to assume a prescribed outer diameter, and then cutting it to prescribed lengths, and polishing the cut faces thereof.
According to this method, since the cylindrical dosimeter glass element can be manufactured by heating and extending a cylindrical glass base material, it is possible to manufacture a dosimeter glass element by a smaller number of manufacturing steps, in a short period of time, and at low cost, compared to cases where it is manufactured by polishing on all faces thereof, as in the prior art. Moreover, since the dosimeter glass element is extended in a circular bar shape, the diameter thereof does not change even if it twists during forming, and hence forming accuracy is improved.
In order to achieve the second object, the present invention provides a dosimeter holder provided so as to be able to accommodate internally a dosimeter element which generates fluorescence corresponding to the radiation exposure dose thereof, comprising: an indication of a fluorescence reading position of said dosimeter element being provided on the outer surface of the dosimeter holder.
According to this dosimeter holder, since the fluorescence reading position is indicated on the outer face of the dosimeter holder, it is possible to position the holder on a measurement subject in such a manner that the dosimeter holder, and hence the dosimeter element, can be aligned with the radiation exposure range and the fluorescence reading range, by using the indication as a reference.